This invention relates generally to devices for preventing the exhaustion of storage batteries utilized as auxiliary and starting power sources for motor-generator sets. In vehicular power systems, it is customary to utilize a fuel-powered motor, such as a gasoline engine, as the primary power source. During normal operation, the electrical load of the vehicle is driven off a generator powered by said motor. Such electrical load may include lights, small electrical motors for operation of auxiliary apparatus and audio equipment such as radios. Such vehicles are generally provided with a storage battery for the purpose of starting the motor and also for the purpose of providing auxiliary power for the electrical devices in the vehicle when the motor is in an off state.
By way of specific example, in an automobile, the electrical appliances might include the various lights (both safety and illumination), an electric defroster, motors for power accessories such as locks and windows, a radio, a stereo, etc. When the motor is on, all of these electrical devices are powered by the generator driven by the motor. When the motor is off, these devices may be powered by the battery, giving rise to the risk that the battery will be drained to a level at which it retains insufficient charge to restart the engine. Such an occurrence can result from the inadvertent leaving of lights or other electrical appliances in an on state when the vehicle is left unattended. Not only does the running down of the battery under such circumstances cause inconvenience, but it may also create safety hazards to the driver and passengers.
By providing a resettable device for automatically cutting off the flow of current from the battery after a predetermined current flow, when the generator is inoperative, the foregoing problems can be overcome.